This invention relates to ultraviolet (UV) light absorbing compounds, polymer compositions and methods for making same. More particularly, the invention relates to UV light absorbing compounds and to polymer compositions including silicone polymers which compositions include, or are partially derived from, such UV light absorbing compounds, and to methods for producing such UV light absorbing compounds and polymer compositions. The subject polymer compositions, which are preferably optically clear, may be used in the fabrication of UV light absorbing ocular devices such as corneal contact lenses, intraocular lenses, and corneal intrastromal implant lenses.
The incident light entering the eye is composed of the entire spectrum of wavelengths including the ultraviolet, visible, and infrared. The cornea preferentially filters UV light in the range of about 300 nm to about 400 nm. Thus, in the eye with its natural lens in place relatively little radiation of wavelengths less that about 400 nm reaches the posterior intraocular structures, e.g., the vitreous humor and the retina.
In the aphakic individual, i.e., that individual who has had the natural crystalline lens removed, there is a loss in protection for the retina from UV light in the above-noted range. Thus, the use of UV light absorbing contact or intraocular lenses is particularly important for the aphakic person. It is further believed that UV light screening spectacles or contact lenses may retard the development of a cataract in the natural lens.
Although low molecular weight, non-polymerizable UV light absorbing compounds of various types are effective in blocking UV radiation when compounded into polymer formulations, their extractability in various media may limit their utility. Also, such UV light absorbing compounds have a potential for phase separation from the polymer formulation. This so-called "blooming" effect is dependent on how soluble the UV light absorbing compound is in the polymer. These problems are remedied by the synthesis of polymerizable, UV light absorbing monomers which can be covalently coupled into the polymer matrix. These covalently bonded UV light absorbing monomers are not extractable and do not phase separate from the remainder of the polymer. Articles fabricated from UV light absorbing silicone compositions incorporating these polymerizable UV light absorbing monomers therefore maintain stable ultraviolet screening characteristics and do not exhibit haze or blooming. The "blooming" problem could be solved by providing a UV light absorbing compound which, even though it is not polymerizable, has increased solubility in the polymer.
Reich, et al U.S. Pat. No. 4,868,251 discloses UV light absorbing compositions comprising silicone elastomers and, covalently bonded thereto, a UV light absorbing component derived from one or more of certain vinyl functional benzotriazole monomers. In preparing the final composition, heat and/or a co-solvent, such as isopropanol, is often needed to dissolve the UV light absorbing monomer in the silicone prepolymer. It would be advantageous to provide a UV light absorbing component which has substantial compatibility or solubility in the solvent. This would simplify, ease and quicken the manufacture of the final UV light absorbing polymeric composition. Further, an UV light absorbing component with enhanced compatibility and/or solubility would result in a monomer/prepolymer mix with a relatively long shelf life so that the mix could be produced and stored well before its ultimate use with little or no phase separation or other detrimental effect.
European Patent Publication No. 0282294 discloses vinylsilylalkoxy arylbenzotriazole monomers which are incorporated into optically clear silicone polymers. These silicon-containing monomers are taught as being more reactable with the silicone polymers than are non-silicon-containing monomers so that a more complete reaction and less non-reacted monomer are obtained. This publication still discloses the need for relatively high temperature, on the order of 90.degree. C., to solubilize the monomer in the silicone prepolymer. Because of these elevated temperatures, the monomer is often mixed with only one portion or part of a conventional two part silicone formulation. The resulting additional mixing step adds to the cost and complexity of the final polymeric composition manufacturing process. Also, the limited solubility of this monomer reduces the effective shelf life of the prepolymer/monomer mixture.
Clearly, it would be advantageous to provide a new, preferably more soluble, class of UV light absorbing compounds, particularly for use in silicone polymers.